Stability Constants, Kstab - exam practice
Stability Constants, Kstab
Question 1 of 3
What is meant by the term stability constant, Kstab?
The table below shows values of the stability constants for the following equilibrium:
[M(H2O)6]n+(aq) + L-(aq) ⇌ [M(H2O)5L](n-1)+(aq) + H2O(l)
where M is one of the metal ions listed and L is one of the ligands which replaces one H2O molecule.
Use the data in the table to predict the formula of the complex formed in the greatest amount when a solution containing equal concentrations of both Cu2+ and Ni2+ ions is added to NH3(aq).
Use the data in the table to predict the formula of the complex formed in the greatest amount when a solution containing equal concentrations of both Hg2+ and Fe3+ ions is added to Cl-(aq).
Use the data in the table to predict the formula of the complex formed in the greatest amount when a solution containing equal concentrations of Cl-, SCN- and F- ions is added to Fe3+(aq).
The diagram below shows the structure of the multidentate ligand ethylenediaminetetraacetate, EDTA4-.
Write an equation for the equilibrium that is established when hydrated chromium(III) ions, [Cr(H2O)6]3+, react with EDTA4- ions to form the complex ion, [Cr(EDTA)]-.
Name the type of reaction occuring in part a).
Write an expression for the stability constant, Kstab, of [Cr(EDTA)]- in this reaction.
State the units of Kstab.
The value of Kstab for this equilibrium is 2.51 × 1023 mol-1 dm3.
Suggest what information can be deduced from the value of Kstab.
Explain why the equilbrium position lies almost completely to the right to form the EDTA complex.
Iron(III) forms complexes in separate reactions with both SCN- ions and Cl- ions.
Equilibrium 1: Fe3+(aq) + SCN-(aq) ⇌ [FeSCN]2+(aq)
Equilibrium 2: Fe3+(aq) + 4Cl-(aq) ⇌ [FeCl4]-(aq)
Write the expressions for the stability constants, Kstab, for these two equilibria.
Give the units of Kstab for both equilibria.
An equilibrium can be set up between these two complexes as shown in equilibrium 3.
Equilibrium 3: [FeCl4]-(aq) + SCN-(aq) ⇌ [FeSCN]2+(aq) + 4Cl-(aq)
Write an expression for Keq(3) in terms of Kstab(1) and Kstab(2).
The values for these stability constants are:
Kstab(1) = 140 mol-1 dm3
Kstab(2) = 0.800 mol-4 dm12
Calculate the value of Keq(3) and state its units.
Give your answer to 3 significant figures.